fix: reuse already loaded world and handle Folia unsupported world creation

src/main/java/dev/loki/loparkour/world/core/World.java

@@ -54,6 +54,11 @@ public class World {
 
         if (Config.CONFIG.getBoolean("world.delete-on-reload")) {
             deleteWorld();
+        } else if (world != null) {
+            // Already loaded (e.g. pre-created by a worlds plugin, required on Folia) — do not recreate.
+            LoParkour.log("Using already loaded world " + name);
+            setup();
+            return;
         }
 
         createWorld();
@@ -71,6 +76,10 @@ public class World {
                     .environment(org.bukkit.World.Environment.NORMAL);
 
             world = Bukkit.createWorld(creator);
+        } catch (UnsupportedOperationException ex) {
+            LoParkour.getPlugin().getLogger().severe(
+                    "World creation is not supported on this server (Folia). Pre-create the world '" + name
+                            + "' with a worlds plugin and restart.");
         } catch (IllegalArgumentException | IllegalStateException ex) {
             LoParkour.getPlugin().getLogger().severe(
                     "Error while trying to create the parkour world — check world.name — " + ex.getMessage());
@@ -130,7 +139,13 @@ public class World {
             return;
         }
 
-        Bukkit.unloadWorld(name, false);
+        try {
+            Bukkit.unloadWorld(name, false);
+        } catch (UnsupportedOperationException ex) {
+            LoParkour.getPlugin().getLogger().severe(
+                    "Cannot unload/delete world on this server (Folia) — set world.delete-on-reload to false.");
+            return;
+        }
 
         try (Stream<Path> files = Files.walk(folder.toPath())) {
             files.sorted(Comparator.reverseOrder())